Materials screeners are used extensively in the landscaping, excavating and materials handling industries to perform such functions as sifting topsoil, separating rocks of different dimensions, and even separating composted materials from compost enhancing materials such as wood chips.
Prior art material screeners suffer from several drawbacks. For example, screeners which employ an inclined screen cannot have an entire front-end bucket loader of material dumped on the screen since the screen is not large enough to process the materials quickly enough and thus, a significant amount of the raw materials will run off the screen, unprocessed. Accordingly, the operator of such a materials screener must slowly dump or release the contents of the raw materials to be screened from the front-end bucket loader onto the vibrating screen.
This process completely ties up the front-end bucket operator and prevents him from retrieving the next bucket load of materials to be screened. Thus, the throughput of the materials screener is significantly impacted and reduced. Moreover, many small portable inclined material screeners such as disclosed in U.S. Pat. Nos. 4,237,000 and 4,197,194 require that the screened material be removed after each bucket of raw material has been processed.
An additional concern is the screening of wet or damp material which may cause "bridges" or blockages in the screen once the materials have been dumped on the screen. Such a problem requires the operator to manually remove the "bridges" or blockages taking a considerable amount of time and greatly affecting screener throughput, while exposing the operator to dangerous moving parts.
In those systems employing an in-feed hopper and in-feed conveyer to supply the raw materials to be screened to a screening deck such as disclosed, for example, in U.S. Pat. No. 3,701,422, such screeners are still restricted in throughput since the screener can only process a limited amount of material at on time. Similar problems of screen "bridging" also exists. An additional drawback is the cost to purchase, maintain, and make available at the site the in-feed hoppers and conveyers to bring materials to the screener.
Finally, all such prior art screeners encounter difficulties when dealing with large objects such as large stones or stumps which are often included in the raw materials to be screened. In order for the prior art screeners to ensure that the screens are not damaged due to these large objects, "grizzly" or "scalping" bars must be provided above the screening area to pre-screen or separate these large objects from the remainder of the material to be screened. These "grizzly" or "scalping" bars add further additional expense to the screeners. Additionally, these bars often get blocked with such rocks or stumps. The blocked rocks or stumps must then be manually removed before operation of the screener can continue.
Accordingly, what is needed is a materials screener which can significantly reduce the time required to dump raw materials to be screened on the screener, which ensures that no material will stick to or "bridge" the screen, and which does not require "grizzly" or "scalping" bars to separate the large rocks and stumps from the remainder of the materials to be screened.